Robotic Vehicle Sensor Development for Internal Detection of Pipeline Defects

Project Number

FEW01-01124

Goal

The goal is to increase the safety, reliability, and integrity of the nation's natural gas infrastructure.

Performer

Sandia National Laboratory (SNL) – project management and research product

Background

The objective of this project is to evaluate emerging sensor technologies that are compatible with an adaptive, controllable, self-propelled, maneuverable robotic vehicle system, and are capable of locating and assessing the severity of internal pipeline defects such as corrosion, stress corrosion cracks, and dents.

Accomplishments (most recent listed first)

Reviewed and summarized state-of-the-art sensor technology,

Evaluated ultrasonic testing (UT), eddy-current (EC), capacitance and electromagnetic acoustic transducer sensors (EMAT) and identified EMAT as the best sensor technology for use with a robotic in-line inspection vehicle, and

When examining the condition of a pipeline, in-line inspection (ILI) utilizing various non-destructive testing (NDT) methods is an essential tool. No NDT technology or technique is universally applicable however, and pipeline operators and inspection service companies jointly choose the appropriate technology for each particular situation. The level of defect specification needed is matched to the performance of the typical inspection tool.

As part of this project, SNL conducted a state-of-the-art review of NDT technologies applicable to defect inspection, and specifically those having the potential for adaptation to in-line pipeline inspection. A report on potentially applicable NDT technologies discussing their potential strengths and weaknesses was submitted in early 2002. Several NDT technologies were reviewed in depth and evaluated for possible use in a robotic in-line inspection system or vehicle. These technologies included ultrasonic testing (UT), eddy current (EC), electromagnetic acoustic transducers (EMAT), and capacitance sensors. Each of these methods was researched and/or investigated for its ability to detect flaws in a natural gas pipeline environment. Their viability, adaptability, strengths, and weaknesses were evaluated as part of this project.

SNL's findings suggest that for a robotic in-line inspection system: (1) UT isn't viable (at this time) for full time 100 percent coverage, (2) EC and capacitance sensors are problematic for this purpose and application, (3) EMAT appears to be the best technology and SNL recommends and supports its use, and (4) industry appears willing to help develop a robotic vehicle compatible with EMAT technology.

SNL has developed a range of un-tethered, autonomously controlled and powered, mobile robotic platforms for surveillance and testing in many environments. This expertise was used to identify potential robotic inspection systems for natural gas pipelines capable of negotiating tight bends, obstructions, varying pipe diameter, and out-of-round sections. Such a system would use existing valves for launch and recovery, generate power from the product flow, and not unduly interfere with product flow. The robotic vehicle concept would be able to regulate its own speed, independent of product speed, and would be able to stop and even reverse motion in the pipe for in-depth, close inspection of detected flaws. Because this vehicle could travel at speeds slower than the gas flow velocity or could stop in the pipe, previously unused NDT technologies could potentially be utilized for better characterization of pipeline defects, corrosion, or damage.

SNL developed several concepts for a robotic, in-line inspection vehicle and a number of general findings were developed related to the impact of the sensors on the design of the vehicle. For example, signal evaluation must be performed on board the robotic vehicle in order to make data storage practical. In addition, if data transmission is to be performed at regular intervals, rather than real time, extensive programming will be required in order to capture the repeated scans performed by the robot when it backs up to a questionable area for closer inspection. Also, a robotic system must be robust enough to offer adequate control within the pipeline environment. If it is too light, the unit could literally be blown away, if it is too heavy it will not be able to negotiate obstacles or reverse its course under limited power. The weight of the inspection system, though much less than that of a standard inspection pig, will likely control the overall weight of the system. It is not expected that any of the sensors evaluated would significantly affect the overall system weight.

The power required for each of the sensor types evaluated is actually quite similar. But until the basic requirements for the electronics system (i.e. the number of transducers, the pulse repetition frequency, operating frequency, extent of onboard data analysis, and the amount of on-board storage) are defined, good estimates are difficult. However, it is estimated that each transducer channel would require between 0.25 and 1.0 watts of power. Since, this is significantly smaller than the power estimated for system propulsion, data evaluation, and data communication elements, the sensor system power requirements should not be a major driver for the power system in a robotic vehicle.